1. Field of the Invention
The present invention relates to a semiconductor device using an insulated gate field-effect transistor.
2. Description of the Related Art
In recent years, a metal oxide having semiconductor characteristics, which is called an oxide semiconductor, has attracted attention as a novel semiconductor material having both high mobility like the mobility of polycrystalline silicon or microcrystalline silicon and uniform element characteristics like the element characteristics of amorphous silicon. The metal oxide has been used for various applications; for example, indium oxide, which is a well-known metal oxide, has been used as a material of a transparent electrode for a liquid crystal display device or the like. Examples of such a metal oxide having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, and zinc oxide. Transistors in each of which a channel formation region is formed using such a metal oxide having semiconductor characteristics are known (Patent Documents 1 and 2).